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fix: allow client connect after close #2581

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merged 6 commits into from
Oct 16, 2020
Merged

fix: allow client connect after close #2581

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8ca579c
allow for client connect after close
HanaPearlman Oct 13, 2020
f7ca2ff
bind withClient to this
HanaPearlman Oct 14, 2020
c5e0309
respond to withClient comment
HanaPearlman Oct 14, 2020
4fe0911
add additional connection expectations in test
HanaPearlman Oct 14, 2020
4c113dd
Merge branch 'master' into NODE-2544/master/fix-connect-after-close
HanaPearlman Oct 15, 2020
09dde51
use MongoError instead of plain Error
HanaPearlman Oct 15, 2020
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16 changes: 13 additions & 3 deletions src/mongo_client.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -346,19 +346,29 @@ export class MongoClient extends EventEmitter implements OperationParent {
const force = typeof forceOrCallback === 'boolean' ? forceOrCallback : false;

return maybePromise(callback, cb => {
const completeClose = (err?: AnyError) => {
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nit: naming of completeClose, perhaps something like resetState is more apt?

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Had a small offline discussion. Leaning towards leaving this as-is because completeClose both resets the state and calls the callback. Does anyone else have thoughts on this?

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I'm fine with completeClose, it's also a pattern we use elsewhere

// clear out references to old topology
this.topology = undefined;
this.s.dbCache = new Map();
this.s.sessions = new Set();

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@HanaPearlman HanaPearlman Oct 14, 2020 •
edited
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Per a discussion from #2355, we don't restore this.s.options to what it was originally constructed with here, so we get output warnings when re-connecting:

the options [servers] is not supported
the options [caseTranslate] is not supported
the options [dbName] is not supported

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I think this is fine for today. There's another unit of work here in the future (after the MongoClientOptions project) where the options will be stored immutably, in which case this problem goes away.

cb(err);
};

if (this.topology == null) {
return cb();
completeClose();
return;
}

const topology = this.topology;
topology.close({ force }, err => {
const autoEncrypter = topology.s.options.autoEncrypter;
if (!autoEncrypter) {
cb(err);
completeClose(err);
return;
}

autoEncrypter.teardown(force, err2 => cb(err || err2));
autoEncrypter.teardown(force, err2 => completeClose(err || err2));
});
});
}
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5 changes: 5 additions & 0 deletions src/operations/connect.ts
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Expand Up @@ -197,6 +197,11 @@ export function connect(
throw new Error('no callback function provided');
}

// Has a connection already been established?
if (mongoClient.topology && mongoClient.topology.isConnected()) {
throw new Error(`'connect' cannot be called when already connected`);
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Let's not use plain Error objects, instead prefer a TypeError for simple type mismatches and MongoError or one of its subclasses for the rest. In this case I think a MongoError would be best. (I know the code right above this uses an Error, but let's be the change we want to see in the world right?)

}

let didRequestAuthentication = false;
const logger = new Logger('MongoClient', options);

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31 changes: 31 additions & 0 deletions test/functional/connection.test.js
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Expand Up @@ -2,6 +2,7 @@
const test = require('./shared').assert,
setupDatabase = require('./shared').setupDatabase,
expect = require('chai').expect;
const withClient = require('./shared').withClient;

describe('Connection', function () {
before(function () {
Expand Down Expand Up @@ -273,4 +274,34 @@ describe('Connection', function () {
done();
}
});

it(
'should be able to connect again after close',
withClient(function (client, done) {
expect(client.isConnected()).to.be.true;

const collection = () => client.db('testReconnect').collection('test');
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collection().insertOne({ a: 1 }, (err, result) => {
expect(err).to.not.exist;
expect(result).to.exist;

client.close(err => {
expect(err).to.not.exist;
expect(client.isConnected()).to.be.false;

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I'd add expect(client.isConnected()).to.be.false; here

client.connect(err => {
expect(err).to.not.exist;
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And another expect(client.isConnected()).to.be.true; here, just as a sanity check.

expect(client.isConnected()).to.be.true;

collection().insertOne({ b: 2 }, (err, result) => {
expect(err).to.not.exist;
expect(result).to.exist;
expect(client.topology.isDestroyed()).to.be.false;
done();
});
});
});
});
})
);
});
4 changes: 2 additions & 2 deletions test/functional/sessions.test.js
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Expand Up @@ -123,7 +123,7 @@ describe('Sessions', function () {
// verify that the `endSessions` command was sent
const lastCommand = test.commands.started[test.commands.started.length - 1];
expect(lastCommand.commandName).to.equal('endSessions');
expect(client.topology.s.sessionPool.sessions).to.have.length(0);
expect(client.topology).to.not.exist;
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what's going on with the changes in this file? It looks like we're losing coverage

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As part of closing the MongoClient, we set client.topology to undefined, so we cannot check the size of its session pool, we can just check that the topology no longer exists.

I agree it's not the best but it seems like we have to set the topology to undefined (instead of just setting the state of the topology to closed) because otherwise it's ambiguous whether the topology 1) just hasn't been opened yet or 2) was closed/all cleaned up.

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Hmm. I think an implicit part of this work is that Topology can be connected, closed and reused as well. A Topology basically is a client, the MongoClient being a wrapper around it to provide access to higher level API. Ideally we would want to assign a Topology in the constructor of MongoClient, rather than during connect (but that's not quite possible today).

Have you tried not resetting topology = undefined yet? This might require changes to the connect operation. Let's not go down a huge rabbit hole here, but I'd like to better understand the limitations to that approach before opting for this alternative.

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@HanaPearlman HanaPearlman Oct 16, 2020 •
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Yep, you're right, it is possible to not set topology = undefined after a small change to the connect logic. This means we don't need to do any additional clean-up on client close, since any references to a Db/Client can use the same topology after re-connect. I've made this change, and will write a few tests to verify that the topology still receives the correct events after client re-connect.

Update: decided against making these changes because of the refactor required to re-connect topologies may be too much work for this ticket.

});
});
});
Expand All @@ -143,7 +143,7 @@ describe('Sessions', function () {
// verify that the `endSessions` command was sent
const lastCommand = test.commands.started[test.commands.started.length - 1];
expect(lastCommand.commandName).to.equal('endSessions');
expect(client.topology.s.sessionPool.sessions).to.have.length(0);
expect(client.topology).to.not.exist;
});
});
}
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